This invention relates to aquarium filtration, and more particularly to improvements in the biological filtration of aquarium water.
Whenever aquatic animals are to be maintained within an aquarium environment, the quality of the water in which thev live must be maintained at a suitable level. In addition to properly controlling the temperature, dissolved oxygen and other water qualities, the toxic material content of the water must be maintained at a sufficiently low level to prevent harm to the tank's inhabitants.
The main source of contaminants within an aquarium are the aquatic animals themselves. The metabolic waste of the aquatic animals is stored within the aquarium. In high concentrations, these waste products become toxic to the same animals that produced them.
To combat the problem of toxic waste build-up, three types of filtration approaches are generally utilized. One approach is physical filtration wherein the suspended waste material is physically trapped by mechanical filters. The filters utilize filtration material in the form of particles of gravel, or fluffy masses of synthetic resin fibers. Sand or gravel beds are well known materials which are also used in undergravel type of filters.
The second well known type of filtration is chemical filtration which relates to the removal or deactivation of mostly organics and any substance containing the element carbon. Activated carbon and ion exchange resins are commonly used materials. While the above forms of filtration are well known and frequently utilized, they are insufficient for purifying the water and eliminating some of the common known toxic waste products of the aquatic animals themselves.
The third type of filtration which is probably the most important and yet least utilized, is that of biological filtration. Such biological filtration is accomplished by means of living organisms, primarily bacteria. The presence of these biologically active bacteria in an aquarium is essential, since they serve to rid the tank of toxic ammonia.
Ammonia is a highly toxic substance harmful to many aquatic animals even if present in very low concentrations. Ammonia toxicity is pH sensitive. The higher the pH, the more toxic the ammonia becomes. Since marine aquariums generally maintain a higher pH than their fresh water counterparts, ammonia levels are of greater concern in the salt water aquarium. However, even in fresh water aquarium tanks ammonia can build up to high levels and cause toxicity in the water.
Ammonia is generated by the animals themselves which excrete ammonia directly. Additionally, ammonia is the end product of decaying organic matter such as uneaten food, dead animals, and feces. The ammonia is removed from the aquarium through biological filtration by a process called "nitrification". Nitrification is a two step process which requires two different types of bacteria to perform each step. These two types of bacteria are referred to as nitrifiers or nitrifying bacteria.
The first step in this sequence is performed by bacteria of the type Nitrosomonas. These bacteria remove ammonia from the water and, through biological oxidation, convert it to a different substance, nitrite. While nitrite is generally less toxic than ammonia, the removal of ammonia still does not provide adequate purification to the water. However, a different group of bacteria, the Nitrobacter bacteria quickly act on the nitrite and convert it further to nitrate, which is harmless to the aquatic inhabitants.
Both of these types of bacteria are of the aerobic form. However, even anaerobic bacteria are useful in reducing the ammonia, although they produce different end products, some of which are toxic to aquatic life. By maintaining an adequate supply of oxygen to the aquarium, the anaerobic bacteria can be kept in check and adequate aerobic bacteria are provided.
The aerobic nitrifying bacteria have two basic requirements to carry out their functions. The first is the need for adequate oxygen concentrations. The second is that they require a place to attach themselves.
Previously, the undergravel filters have been frequently utilized as a simple way of supplying the needs of these aerobic bacteria. The filter draws in oxygenated water through a gravel bed to which bacteria have attached themselves. While such gravel beds have been ideal for bacterial growth, they have apparent limitations. For example, there is a limit to the amount of gravel surface that can be supplied. This limit is basically the area of the aquarium base. The gravel, deep beneath the bed, retains limited numbers of aerobic bacteria. Furthermore, the depth of the gravel bed is limited by aesthetic requirements and by the height of the aquarium. Furthermore, while smaller gravel grain size is one way of supplying more surface area for the attachment of bacteria, the presence of the small gravel grains tends to clog the filter, and blocks the water passages through the gravel.
Accordingly, aquariums have heretofore presented limited surface areas upon which the aerobic bacteria can attach themselves and propagate.